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Chem. Mater. 1996, 8, 751-761
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New Quaternary Compounds Resulting from the Reaction of Copper and f-Block Metals in Molten Polychalcogenide Salts at Intermediate Temperatures. Valence Fluctuations in the Layered CsCuCeS3 Anthony C. Sutorik,† Joyce Albritton-Thomas,‡ Tim Hogan,‡ Carl R. Kannewurf,‡ and Mercouri G. Kanatzidis*,† Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, and Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, Illinois 60208 Received September 19, 1995. Revised Manuscript Received January 10, 1996X
From the reaction of elemental copper and either lanthanides or actinides in molten alkali metal/polychalcogenide salts, several new quaternary phases have been discovered. Specifically, these phases are ACuM2Q6 (where A ) K, M ) La, Q ) S; A ) Cs, M ) Ce, Q ) S; or A ) K, M ) Ce, Q ) Se) and ACuMQ3 (where A ) Cs, M ) Ce, Q ) S; or A ) K, M ) U, Q ) Se). The CsCuCe2S6 crystallizes in the orthorhombic space group Immm with a ) 5.500(1) Å, b ) 22.45(1) Å, c ) 4.205(4) Å. The KCuCe2Se6 is isostructural. The CsCuCeS3 crystallizes in the orthorhombic space group Cmcm with a ) 4.024(2) Å, b ) 15.154(2) Å, c ) 10.353(3) Å. The KCuUSe3 is isostructural. In ACuM2Q6, the lanthanides bond to a mixture of mono- and disulfides in a bicapped trigonal prismatic geometry; these polyhedra subsequently connect in two dimensions, forming layers equivalent to those seen in the ZrSe3 structure type with Cu+ atoms residing in tetrahedral sites within the layers and alkali cations in the interlayer gallery. The compounds of the formula ACuMQ3 also possess a layered structure. Here the [MQ6] octahedral units form corrugated, two-dimensional sheets via edge-sharing in the first dimension and corner-sharing in the second. Copper cations are coordinated to tetrahedral sites in the folds of the corrugations, and alkali cations are again in the intergallery region. Details of the synthesis, structure, and properties of these compounds are discussed.
A. Introduction The reactions of lanthanides in A2Qx fluxes have led to new phases which repeat several structural themes seen in known binary and ternary chalcogenides.1 The next question to be asked is how can the reaction of these metals be modified in order to access phases which are less structurally related to known compounds and so more likely to feature new and novel characteristics. The simplest approach is to react another element, such as a transition metal, in the A2Qx flux along with the lanthanide or actinide with an eye toward forming new quaternary compounds. The extra element would be chosen such that its coordination chemistry is very different from that of the f-block metal. Thus, when the two metals come together in a new compound, the interplay of dissimilar structural and coordination requirements should help to maximize the probability that any new phases would be clear departures from what has been seen before. Investigations into quaternary systems with lanthanides and actinides are of particular interest because of the intriguing structural and physical properties which have been known to †
Michigan State University. Northwestern University. X Abstract published in Advance ACS Abstracts, February 15, 1996. (1) (a) Sutorik, A. C.; Kanatzidis, M. G. J. Am. Chem. Soc. 1991, 113, 7754-7755. (b) Sutorik, A. C.; Kanatzidis, M. G. Angew. Chem., Int. Ed. Engl. 1992, 31, 1594-1596. (c) Sutorik, A. C. Kanatzidis, M. G., submitted for publication. ‡
result from the interplay of covalent transition-metal bonding and the more ionic lanthanide and actinide bonding. For example, the most notable high-Tc copper oxide superconductors are compounds containing heterometallic mixtures of highly electropositive cations (i.e., Tl2Ba2Ca2Cu3O102a and La2-x(Ca, Sr, Ba)xCuO42b,c). It has been speculated that these cations have an inductive effect on the anionic Cu-O framework resulting in subtle changes in the covalency of those bonds which in turn impacts the critical temperature.2,3 In the complicated cooperative environment of a solid-state material, there are many effects in which the cations may participate. A better understanding of the interplay of these effects could be achieved if a wider base of compounds containing mixtures of highly electropositive cations were available for study. As such we have been interested in searching for such compounds in quaternary systems containing the chalcogenide elements. Many examples already exist of quaternary compounds isolated from reactions in molten A2Qx fluxes. Some systems have even been refined to the point where certain species can be formed reproducibly in situ and then used as ligands to the remaining metal cations in (2) (a) Sleight, A. W. Chemistry of High-Temperature Superconductors; ACS Symposium Series 351; American Chemical Society: Washington DC, 1987; Chapter 1, p 2. (b) Sheng, Z. Z.; Herman, A. M. Nature 1988, 332, 138-139. (c) Parkin, S. S.; et. al. Phys. Rev. Lett. 1988, 61, 750-753. (3) (a) Bednorz, J. G.; Muller, K. A. Z. Phys. 1986, B64, 189-193. (b) Cava, R. J.; vanDover, R. B.; Batlogg, B.; Reitman, E. A. Phys. Rev. Letts. 1987, 58, 408-410.
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the flux. This approach has worked well in several quaternary systems where the fourth element is a nonmetal. The anion (TeS3)2-, which was employed as a ligand for the first time from a molten salt reaction,4 and several thiophosphate and selenophosphate species have been isolated from the reaction of a metal and P2Q5 in excess A2Qx flux.7-9 Mixed-metal reactions with Sn as one of the components have led to the characterization of phases in which either (SnS4)4- or (Sn2S6)4- act as thiometalate ligands to the second metal.10 A substantial body of work also exists where quaternary phases have been isolated from molten A2Qx the bulk of which has involved mixed metal reactions between Cu and early-transition-metal elements.11-16 Recently, this work has been expanded into transition metal/ f-block chemistry as well with the reporting of the compounds BaLnMQ3 (Ln ) La, Ce, Nd; M ) Cu, Ag; Q ) S, Se),17 KLnMQ4 (Ln ) La, Nd, Ga, Y; M ) Si, Ge; and Q ) S, Se),18 CsCuUTe3,19a and CsTiUTe5.19b In attempting to develop similar quaternary chemistry with the f-block elements at intermediate temperatures (250-450 °C), several heterometallic systems were investigated. Of these systems the reactions using Cu were highly successful at providing new quaternary phases. Two new structure types have already been reported: KCuCe2S6 and K2Cu2CeS4.20 This report details the synthesis, structures, and properties of five new quaternary chalcogenides. Three of them are additions to the KCuCe2S6 family (KCuLa2S6, CsCuCe2S6, KCuCe2Se6) and two more phases (CsCuCeS3 and KCuUSe3) are isostructural to the known ACuMQ3 structure type (A ) alkali metal, M ) 4+ transition metal, Q ) chalcogenide).15,16 B. Experimental Section 1. Synthesis. Reagents. The following reagents were used as obtained: copper metal, Fisher Scientific Co., Fairlawn, NJ; cerium, 40 mesh, Johnson M. Matthey Co., Ward Hill, MA; uranium metal, 60 mesh, Cerac, Milwaukee, WI; lanthanum, 40 mesh, Cerac, Milwaukee, WI; selenium powder, 100 mesh, Aldrich, Milwaukee, WI; sulfur powder, sublimed, JT Baker Co., Phillipsburg, NJ; potassium metal, analytical reagent, Mallinckrodt Inc., Paris, KY; sodium metal, analytical reagent, Mallinckrodt Inc., Paris, KY; cesium metal, Johnson M. (4) McCarthy, T.; Zhang, X.; Kanatzidis, M. G. Inorg. Chem. 1993, 32, 2944-2948. (5) Zhang, X.; Kanatzidis, M. G. J. Am. Chem. Soc. 1994, 116, 1890-1898. (6) Zhang, X.; Kanatzidis, M. G. Inorg. Chem. 1994, 33, 1238-1240. (7) McCarthy, T. M.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 10611063. (8) McCarthy, T. M. Ph.D., Michigan State University, 1994. (9) (a) McCarthy, T. M.; Kanatzidis, M. G. J. Chem. Soc., Chem. Commun. 1994, 1089-1090. (b) McCarthy, T. M.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257-1267. (10) Liao, J.-H.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 15611569. (11) Lu, Y.-J.; Ibers, J. A. Inorg Chem. 1991, 30, 3317-3320. (12) Lu, Y.-J.; Ibers, J. A. J. Solid State Chem. 1991, 94, 381-385. (13) Lu, Y.-J.; Ibers, J. A. J. Solid State Chem. 1993, 107, 58-62. (14) Lu, Y.-J.; Ibers, J. A. J. Solid State Chem. 1992, 98, 312-317. (15) Mansuetto, M. F.; Keane, P. M.; Ibers, J. A. J. Solid State Chem. 1992, 101, 257-264. (16) Mansuetto, M. F.; Keane, P. M.; Ibers, J. A. J. Solid State Chem. 1993, 105, 580-587. (17) (a) Christuk, A. E.; Wu, P.; Ibers, J. A. J. Solid State Chem. 1994, 110, 330-336. (b) Wu, P.; Christuk, A. E.; Ibers, J. A. J. Solid State Chem. 1994, 110, 337-344. (18) Wu, P.; Ibers, J. A. J. Solid State Chem. 1993, 107, 347-355. (19) (a) Cody, J. A.; Ibers, J. A. Inorg. Chem. 1995, 34, 3165-3172. (b) Cody, J. A.; Mansuetto, M. F.; Chien, S.; Ibers, J. A. Mater. Sci. Forum 1994, 152-153, 35-42. (20) Sutorik, A. C.; Kanatzidis, M. G. J. Am. Chem. Soc. 1994, 116, 7706-7713.
Sutorik et al. Matthey Co., Ward Hill, MA; dimethylformamide (DMF), analytical reagent grade, EM Science, Inc., Gibbstown, NJ; methanol, anhydrous, analytical reagent grade, Mallinckrodt Inc., Paris, KY. Potassium Selenide, K2Se. The following procedure was modified from that given in the literature.21 An amount of 4.976 g (127.3 mmol) K was sliced in an N2-filled glovebox and combined with 5.024 g (63.6 mmol) of Se into a 250 mL roundbottom flask. The flask was chilled to -78 °C using a dry ice/ acetone bath and approximately 100 mL of NH3 was condensed, under an N2 atmosphere, onto the reagents, giving a dark blue solution. The solution was stirred with a magnetic stir bar while the liquid NH3 was allowed to slowly evaporate off as the reaction warmed to room temperature under a flow of N2 (approximately 8 h). A second portion of NH3 is usually added, and the evaporation repeated to ensure complete reaction of the reagents. The resulting light orange product is evacuated on a Schlenk line overnight and then taken into an N2-filled glove box where it is ground to a fine powder and stored. Potassium sulfide (a pale yellow powder) was prepared and handled similarly. Cesium Sulfide, Cs2S. In an N2-filled glovebox, 10.089 g (75.9 mmol) of Cs (caution: fire and explosion hazard if in contact with air or protic solvents!) is weighed into a 250 mL three-neck round-bottom flask. Two of the necks are stoppered, and the remaining one is connected to a glass adapter with a stopcock joint. The apparatus is removed from the box and connected to a coldfinger condenser adapted to allow for N2 flow. The flask is chilled to -78 °C using a dry ice/acetone bath, and approximately 100 mL of NH3 is condensed, under an N2 atmosphere, onto the Cs, giving a dark blue solution. One of the flask stoppers is gently removed and, with N2 flow maintained, a magnetic stir bar is added to the solution, followed by 1.217 g (38.0 mmol) of S once the solution is stirring. The remainder of the reaction proceeds as described above, resulting in a pale yellow product which was ground to a fine powder and stored in an N2-filled glovebox. KCuLa2S6. Amounts of 0.110 g (1.0 mmol) of K2S, 0.016 g (0.25 mmol) of Cu, 0.069 g (0.50 mmol) of Ce, and 0.128 g (4.0 mmol) of S were weighed into a vial in an N2-filled glovebox. The starting materials were mixed thoroughly and loaded into a Pyrex tube. The tube was then evacuated to
